In a pipe through which a fluid such as a gas or a liquid flows, a flow rate control device for controlling the flow rate of the fluid is arranged. For example, as disclosed in Japanese Laid-Open Patent Publication No. 2011-043196, a flow rate control device (flow rate control valve) includes a flow passage disposed in the interior of a valve housing to which a pipe is connected, and the flow passage is opened and closed by a needle valve element. The flow rate of the fluid that flows through the flow passage is controlled by the degree of opening of the needle valve element.
Further, the flow rate control device includes, as a structure for operating the displacement (movement) of the needle valve element, an operating member that is capable of rotating integrally with the needle valve element and on which teeth are formed on a side surface thereof, a gear that is meshed with the teeth, and an indication ring meshed with the gear and having graduations showing the number of rotations of the needle valve element. More specifically, when the user rotates the operating member, a rotational force thereof is transmitted to and rotates the indication ring through the gear, whereby the user can confirm the number of rotations of the needle valve element corresponding to the displacement of the indication ring.
Incidentally, concerning the flow rate control device disclosed in Japanese Laid-Open Patent Publication No. 2011-043196, for minimizing the size thereof, a structure is provided in which the center of rotation of the operating member is matched with the center of rotation of the indication ring, and the gear is interposed between the operating member and the indication ring. However, with this structure, when the indication ring is rotated, the rotational force is transmitted through two gear members, so that the mechanical meshing error is large, and a problem arises in that the indication accuracy is lowered. Further, since the number of parts that make up the flow rate control device is large, there are disadvantages in that the manufacturing cost increases, and further, work efficiency at the time of assembly is reduced.